It is known that molding by injection of resin at low pressure (a process commonly called RTM) is a method for putting composites materials into form, in which a thermosetting resin is injected at low pressure, through a textile preform constituted by reinforcements and which is placed in a closed mold. According to this method, a preform is first of all draped which is placed in the mold, the mold is filled with resin, polymerization of the resin is carried out and the composite part obtained is removed from the mold.
This type of molding may present difficulties in particular in the case of molding by injection of a complex part, of large size and which has vertical lateral walls, such as an aircraft undercarriage bay.
In this type of part, the inside surfaces of the vertical lateral walls have regions of increased thickness for the stiffening of the part. Producing a corresponding preform is difficult to do directly in the mold, in particular for reliable production of the regions of increased thickness, the draping then being carried out blind.
When preforms are produced outside the mold then mounted in the mold, the putting in position of the preforms relative to each other (lateral preforms corresponding to the lateral walls of the part, upper preform, etc.) is difficult to ensure on account of the lower stiffness of those preforms before the injection of resin.
In both these cases, the removal from the mold of the part obtained is rendered complex due to the negative draft angles generated by the regions of increased thickness of the inside surfaces of the lateral walls.